In a number of animal tumor systems, interferon and interferon inducers have shown to possess anti tumor effects. Although several mechanisms have been offered as explanations for this finding, no single explanation for the observations presently exists. Moreover, in certain systems, interferon inducers have been shown to enhance tumor growth. It is well known that certain interferon inducers, notably poly I:C, are potent immunological adjuvants. On the other hand, depletion of circulating lymphocytes, thymic atrophy, and decreased numbers of antibody forming spleen cells have been reported in animals treated with interferon or interferon inducers. The tumor enhancing properties of these agents in certain situations could be the result of an adverse effect on tumor immunity. The present studies will be divided into two parts. One portion will attempt to elucidate the mechanism whereby interferon treatment suppresses the in vitro reaction of lymphocytes to mitogens. The other portion of te study will address itself to sequential studies of lymphocytes derived from patients receiving interferon inducers. Lymphocytes will be obtained from patients prior to and at several times following the administration of the inducer. In vitro cultures of these cells will be prepared for measurement of protein, RNA and DNA synthesis following exposure to plant mitogens, allogeneic lymphocytes and common bacterial and viral antigens. These studies will be correlated with the results of skin testing and the development of cellular and humoral immunity to a new antigen, keyhole limpet hemocyanin. An attempt will be made to relate changes in the above parameters of lymphocyte function to the response manifested to the new antigen. The object of these investigations is to provide a rational foundation upon which to build programs of immunotherapy in human neoplasia.